2 files changed, 12 insertions, 0 deletions
diff --git a/Lib/pkgutil.py b/Lib/pkgutil.py
index e37ad45..9180eae 100644
--- a/Lib/pkgutil.py
+++ b/Lib/pkgutil.py
@@ -119,6 +119,9 @@ def iter_modules(path=None, prefix=''):
     """
     if path is None:
         importers = iter_importers()
+    elif isinstance(path, str):
+        raise ValueError("path must be None or list of paths to look for "
+                        "modules in")
     else:
         importers = map(get_importer, path)
 
diff --git a/Lib/test/test_pkgutil.py b/Lib/test/test_pkgutil.py
index fc04dcf..2887ce6 100644
--- a/Lib/test/test_pkgutil.py
+++ b/Lib/test/test_pkgutil.py
@@ -176,6 +176,15 @@ class PkgutilTests(unittest.TestCase):
                 continue
             del sys.modules[pkg]
 
+    def test_walk_packages_raises_on_string_or_bytes_input(self):
+
+        str_input = 'test_dir'
+        with self.assertRaises((TypeError, ValueError)):
+            list(pkgutil.walk_packages(str_input))
+
+        bytes_input = b'test_dir'
+        with self.assertRaises((TypeError, ValueError)):
+            list(pkgutil.walk_packages(bytes_input))
 
 
 class PkgutilPEP302Tests(unittest.TestCase):